Many microwave popcorn popping constructions in common commercial use are multi-ply paper bags in which inner and outer paper sheets are laminated to one another, with a microwave interactive construction (sometimes referred to as a microwave susceptor) encapsulated between the paper plies. Popcorn popping bags of this type are described, for example, in U.S. Pat. Nos. 4,904,488; 4,973,810; 4,982,064; 5,044,777; and 5,081,330, the disclosures of which are incorporated herein by reference.
A common feature of such constructions is that they are generally made from flexible paper materials. In this manner, the constructions are sufficiently flexible to open or expand conveniently under steam pressure, when a popcorn charge therein is exposed to microwave energy in a microwave oven. Also the materials are sufficiently flexible to be formed from a sheet into a folded configuration, for example during a continuous bag-construction process.
Many microwave popcorn products include, within the bag, a charge of unpopped popcorn kernels, fat/oil (i.e. grease) and flavor (for example salt). During storage or shipment, especially if the environment becomes relatively hot, the material stored within the bag can become liquefied and leak through the bag construction. Even when relatively high temperatures are not encountered in storage, some leakage can occur if the stored material includes a significant amount of flowable or liquefied oil/fat.
In addition, conventional microwave cooking of popcorn (especially when the popcorn charge includes fat/oil) results in the generation of hot liquid oil or fat. If the construction retaining the popcorn charge is paper, the paper must be sufficiently resistant to staining and to the passage of hot liquid oil/fat therethrough, during the microwave cooking process, to be satisfactory for performance of the product. For-example, the oil/fat should not leak from the construction, when the microwave cooking (i.e. popping) is undertaken, sufficiently to generate an undesirable greasy feel or appearance, to the outside of the package.